We had some special cases to handle things like

  case (scc c (case E of alts)) of alts'

but it only worked when there was a single scc in the way.  This
generalises the optimisation to handle multiple sccs and ticks, so
that we can catch most case-of-case optimisations that would normally
apply in the absence of profiling.

This fixes the example in #5363, and nofib results (with -prof
-fprof-auto) show that allocation universally goes down or stays the
same.